A predetermined table where pieces of control data of each type (each message unit) are grouped and correlated with one another is stored in a correlation storage section (105). A control data synchronizing section (104) accumulates inputted control data sequentially in a control data accumulating section (106). The control data synchronizing section (104) groups a plurality of pieces of control data, correlates them with one another with reference to the table stored in the correlation storing section (105), and accumulates them. The pieces of control data are multiplexed through these operations and handled as a piece of data in units of a group. A control data processing section (107) generates the control data multiplexed for each group as a packet and transmits it to the communication party.